1. Field of the Invention
This invention relates to 3,3',5,5'-tetra-substituted diphenoquinones. In one aspect, this invention relates to a process of preparing said tetra-substituted diphenoquinones by oxidatively coupling 2,6-disubstituted phenol in an alkaline reaction medium. In another aspect, this invention relates to said process catalyzed by a phase-transfer catalyst.
2. Description of the Prior Art
Filbey, U.S. Pat. No. 2,905,674, teaches preparing 3,3',5,5'-tetraalkyldiphenoquinones by contacting, in a substantially homogeneous liquid system and under reaction conditions, a 4-halo-2,6-dialkylphenol and a basic compound having an ionization constant characteristic of a base of at least about 1.6 .times. 10.sup.-3 at 25.degree. C. The halogen of said phenol has an atomic weight greater than 30 and at least one of the alkyl groups of said phenol is branched. Equimolar amounts of said basic compound and said phenol are used.
Hay, U.S. Pat. Nos. 3,210,384, 3,306,874 and 3,306,875, teaches a process for preparing tetra-substituted diphenoquinones by reacting oxygen with a solution of a 2,6-disubstituted monohydric, monocyclic phenol dissolved in a suitable inert solvent in the presence of a dissolved oxygen-carrying intermediate comprising a basic cupric salt complex of an organic nitrogen-containing compound selected from the group consisting of cyano-substituted hydrocarbons and N,N-di(monovalent hydrocarbon) carbamoyl substituted hydrocarbons. The oxygen-carrying intermediate is also referred to as an amine-basic cupric salt complex.